Such apparatus is known (Magazine "Bander, Bleche, Rohre", Volume 12, 1971, No. 10, pages 453 and 454). With such apparatus the scraping effect of the nozzles can be ajusted without the temperature and the layer thickness of the air between the strip and measuring device (which varies constantly as a result of the pulsation of the strip) leading to errors in measurement. A solution to the problem of the action of heat on the measuring device is not given in this publication.
In another known similar device (Nuclear Techniques in the Basic Metal Industries, International Atomic Energy Agency, Vienna, 1973, P. 299-317, especially P. 305, FIG. 5) the scraping effect, inter alia, is also adjusted by regulation of the distance of the scraping nozzles from the strip. Here also errors in measurement as a result of change in temperature and change in the layer thickness of the air between the measuring device and the pulsating band do not occur. In order to protect the measuring devices from excessive heat, they are arranged downstream of a cooling tower i.e. at a position where the metal strip has cooled down. Because of this great distance between the location of measurement and the controllable variable (layer thickness) and the place of adjustment (nozzles) the regulating speed is correspondingly slow.
A similar arrangement is also shown in U.S. Pat. No. 3,499,418.
It has already been attempted to employ devices close to the nozzles, and consequently to the place of adjustment, which can tolerate relatively high heat without being damaged, e.g. a beta-ray reflectometer (German Offenlegungsschrift 1,796,303). However, no satisfactory results have been achieved with such a device because the measurements made by the device were not sufficiently precise. The values measured by such a device are distorted both by the temperature of the air between the measuring device and the strip and by the layer thickness of the air between the strip and the measuring device which can scarcely be controlled and which alters constantly as a result of the pulsation of the strip.